1. Field of the Invention
The present invention generally relates to a wheel support bearing assembly for supporting a wheel that is used in, for example, an automotive vehicle and, more particularly, to the wheel support bearing assembly that is coupled with a knuckle made of an aluminum alloy and designed to have a reduced weight.
2. Description of the Prior Art
A wheel support bearing assembly for rotatably supporting a wheel relative to an automobile suspension system has now come to be manufactured with its weight reduced aiming an increase of the mileage accomplished by an automotive vehicle. In an effort to further reduce the weight of the knuckle, the use of the knuckle made of an aluminum alloy, in place of the knuckle made of, for example, malleable cast iron, has in recent years increased as well as slimming the knuckle with extra wall thickness reduced as much as possible.
Since the aluminum alloy has a density that is about one third of that of steel, and even though the knuckle made of the aluminum alloy is manufactured to have a thick walled structure for the purpose of compensating for reduction in rigidity of the aluminum alloy as compared with that of steel, the knuckle made of aluminum alloy can have a weight that is at least half the weight of the conventional knuckle made of steel. Also, as a result of advance in the art of casting, formation of cavities resulting from difference in wall thickness, which has hitherto been considered a problem peculiar to the aluminum alloy, has now come to be suppressed to such an extent that the strength thereof will not be adversely affected. In view of these factors, the aluminum alloy knuckle is expected to be used widely in the near future.
FIG. 5 illustrates the conventional wheel support bearing assembly in a fragmentary longitudinal sectional representation, in which only one of longitudinal halves thereof is shown. The illustrated wheel support bearing assembly is an inner race rotating type of a, so called, third generation and is specifically used for the support of a driven wheel. The wheel support bearing assembly shown therein includes an outer member 31 of one-piece construction including a vehicle body fitting flange 31a formed integrally with an outer periphery thereof so as to extend radially outwardly therefrom, an inner member 32 made up of a hub wheel 32A and a separate inner race forming member 32B mounted firmly on one end of an outer peripheral surface of the hub wheel 32A, and dual rows of rolling elements rollingly accommodated within an annular working space delimited between the inner and outer members 32 and 31. While the outer member 31 has axially spaced apart raceways 34 defined in an inner peripheral surface thereof and the inner member 32 has similarly axially spaced apart raceways 35 defined in an outer peripheral surface thereof, the rows of the rolling elements 33 within the annular working space are received in part within the raceways 34 in the outer member 31 and in part within the raceways 35 in the inner member 32, respectively.
The hub wheel 32A forming a part of the inner member 32 has an outboard end formed integrally with a wheel mounting flange 32a protruding radially outwardly therefrom and a wheel (not shown) is fitted to the wheel mounting flange 32a by means of a plurality of bolts 48. On the other hand, the vehicle body fitting flange 31a integral with the outer member 31 is firmly coupled by means of a bolt 49 with a knuckle 44 that is made of an aluminum alloy and rigidly secured to the vehicle body structure, to thereby allow the wheel to be rotatably supported by the knuckle 44.
The annular working space delimited between the inner and outer members 32 and 31 has inboard and outboard open ends opposite to each other, which are sealed by respective sealing members 37 and 38 to thereby avoid leakage of a lubricant grease filled inside the bearing assembly and also to avoid ingress of rain drops, dusts and dirt into the annular working space.
While the use of the aluminum alloy knuckle 44 contributes to reduction in weight, a potential difference tends to develop between the aluminum alloy used as a material for the knuckle 44 and the steel used as a material for the outer member 31. Because of this, a galvanic cell tends to develop when a surface of the outer member 31 that is held in contact with the knuckle 44 is wetted by muddy brackish water, resulting in electrocorrosion taking place in that contact surface. Once this electrocorrosion occurs, the outer member 31 and the knuckle 44 may be interlocked with each other at that surface where electrocorrosion occurs, hampering the workability during inspection and repair. Although the electrocorrosion can be prevented if an electric insulating material is interposed between the outer member 31 and the knuckle 44, the use of the electric insulating material is an addition to the number of component parts and, therefore, not only does the parts control tend to be complicated, but complicated assembly procedures would be required to connect the wheel support bearing assembly to the knuckle.
As is well known to those skilled in the art, electrostatic charge is built up in the wheel tire during run of the automotive vehicle. This electrostatic charge is conducted to the vehicle body structure through the wheel support bearing assembly made of the inner member 32, the rolling elements 33 and the outer member 31, and then through the knuckle 44. In the event that films of the lubricant oil present between the raceways 35 in the inner member 32 and the rolling elements 33 or between the raceways 34 in the outer member 31 and the rolling elements 33 are insufficient, sparks tend to be induced by the electrostatic charge at the interfaces between the raceways 35 in the inner member 32 and the rolling elements 33 or between the raceways 34 in the outer member 31 and the rolling elements 33, which sparks lead to a cause of generation of noises from a vehicle mounted radio receiver set.